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ahmad_faraz
2 Bronze

How to create snap session for the standard device of 128GB(4way meta).. in 5773

How  to create snap session for the standard device of 128GB(4way meta)?

I am little bit confused here.

1)What should be VEDV side and how to determine that

2)Can i use multiple vdev for onesource in this case.

3) Can i use multiple save devices in  one pool.and how to determine the size of save devices.

In my case  if i require only one snap session can i use one source which can have multiple vdevs and which inturn have multiple Save devices

Any suggestion are welcomed and much appretiated .

Regards

Faraz

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8 Replies
dynamox
6 Thallium

Re: How to create snap session for the standard device of 128GB(4way meta).. in 5773

1) VDEV size and construct should be identical as the source device. If standard device is a 4 way striped meta, you need to build a 4 way striped meta using VDEV devices (meta members the same size)

2) yes, depends on the code

3) save devices can be any size, they don't have to match source devices.

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ahmad_faraz
2 Bronze

Re: How to create snap session for the standard device of 128GB(4way meta).. in 5773

Ok

when you say" we can have multiple vdev for onesource in this case."

Does that mean we can have multiple snap copies of same source .so if i have two vdevs i can present two vdevs to two different host.

what can be the raid type of SAVE device.

Can same save device be pulled in two different pools.

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dynamox
6 Thallium

Re: How to create snap session for the standard device of 128GB(4way meta).. in 5773

ahmad.faraz@hp.com wrote:

Ok

when you say" we can have multiple vdev for onesource in this case."

Does that mean we can have multiple snap copies of same source .so if i have two vdevs i can present two vdevs to two different host.

yes

what can be the raid type of SAVE device.

Can same save device be pulled in two different pools.

device can only belong to one pool, you can use mirror, raid-5 ..i have not tried to use raid-6.

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Quincy561
4 Tellurium

Re: How to create snap session for the standard device of 128GB(4way meta).. in 5773

It is very important that the SAV pool be able to keep up with the write rate to the sorce devices at the time the snap is activated. At that time the SAV pool will see 100% writes at the rate at which the source devices are being written to.

This is why RAID1 is best for the SAV pool, and the best configuration is a little bit of SAV capacity on every spinning disk of a given speed in the system. Another important point is every disk should have the same SAV capacity. If one disk has twice as many SAV devices, it will received twice the load from the snap.

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ahmad_faraz
2 Bronze

Re: How to create snap session for the standard device of 128GB(4way meta).. in 5773

So i understand the save devices can be of any capacity but is there any minimum size of save device.

If yes ,is there calculation/maths  required

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Quincy561
4 Tellurium

Re: How to create snap session for the standard device of 128GB(4way meta).. in 5773

No minimum size. 

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Rasmmacias
2 Iron

Re: How to create snap session for the standard device of 128GB(4way meta).. in 5773

Hello.

SAV device Characteristics

lAs a starting point configure the pool roughly 30% of the capacity of the standard volumes

Increase pool size by an additional 10% as a safety buffer.  (3% of the original capacity.)

lCalculate the number of SAV devices as a proportion of VDEV’s

Eg. 20% track change rate with 882 Vdevs = .20 * 882 = 176 SAV devices

Eg. 30% track change rate with 400 Vdevs = .30 * 400 = 120 SAV devices

lSAV devices can be added online to the pool as net new devices.

Cannot convert a FBA, CKD, BCV device into a SAV device online.

SAV devices are larger than the their standard counterparts
so trying to create a SAV device that isn't the last split on the drive may try to overlap
the next hyper volume.  (
Symmwin will warn you.)

lThere are potentially 3 SAV pools.   FBA, 3390 & 3380 which can’t share storage capacity.

lSAV devices in a pool may be a different size but must have the same protection.

It is recommended to make them the same size

Different pools can have different protection. 

lSpread SAV devices as broadly as possible across available hardware for load balancing.

By default SAV devices are striped across the pool

lSAV devices are not host addressable.

SAV devices store the original track from the standard.

copy takes place on the first write to that track.

lSAV device track counts must be equal or smaller than the largest VDEV.

Symmwin will catch this

lDon’t use Meta volumes for SAV devices.

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Rasmmacias
2 Iron

Re: How to create snap session for the standard device of 128GB(4way meta).. in 5773

lDetermining the Change Track Rate

Change Tracker is a free SE tool.

Change Tracker should be run for each interval snaps are planned.

In the Absence of change tracker information assume the change track rate is 30% as mentioned earlier.

Example: Customer has 200 x 18414 vols and requests 2  VDEV’s for each.
                  Our change track rate was found to be 20%

Number of VDEVS      =  # Standards * # Sessions                                                    ( 200 *  2 = 400 )

Number of SAV devs = Change Rate * # Vdevs                                                        ( 0.2 * 400 = 80 )

Size of SAV devs   = # Vdevs * Cyl Size * Change Rate + safety / # SAV devs  ( 400 * 18414 * 0.2 * 1.1 / 80 = 20255 )
             So we configure 400 x 18414 VDEV’s and  80 x 20255 SAV devices.
(No this breaks the rule that says  SAV devices must be equal or smaller than the Largest Vdev)

         So we configure 400 x 18414 VDEV’s and 88 x 18414 SAV devices.

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